The present invention relates to methods and apparatus for determining, in dependence on the driving situation, the sensitivity of the triggering of an automatic braking operation for a motor vehicle.
An automatic braking operation is described, for example, in DE 40 28 290 C1 where the triggering of an automatic braking operation in a motor vehicle occurs during a braking manoeuvre when the speed of actuation of the brake pedal exceeds a predetermined threshold value. The automatic braking operation consists in producing a brake pressure higher than that corresponding to the position of the brake pedal.
Unpublished German patent application DE-P. 43 25 940.5 discloses the adaptation of the sensitivity of the triggering of the automatic brake operation to vehicle speed and brake pedal position. These adaptations mainly take into account the customary behavior of drivers and are independent of the momentary traffic situation. To vary the threshold value for the speed of actuation, the factors used are obtained from a characteristic diagram in dependence on vehicle speed and brake pedal position.
Adaptation to the individually varying behavior of different drivers by way of characteristic diagram regulation of the triggering criterion in dependence on previous braking manoeuvres, without triggering of the automatic braking operation, is in addition described in unpublished German patent application DE-P. 43 38 068.9. On the basis of the actuation of the pedal in target braking, in which the driver actuates the brake pedal such that the vehicle comes to rest in a position predetermined by the driver, the sensitivity of the triggering of the automatic braking operation, in which the driver wishes to halt the vehicle as quickly as possible, is adapted to the driver.
An object of the present invention is to adapt the sensitivity of triggering of the automatic braking operation to the driving situation existing at the moment of the braking manoeuvre in question and thus to permit better differentiation between emergency braking, in which the automatic braking operation is to be triggered, and target braking in which the triggering of the automatic braking operation is not desired.
This object has been achieved according to the present invention by variation of the sensitivity of the triggering in dependence on the nature, or the time-wise occurrence, of the actuation of the pedal by the driver. In particular, use is made for this purpose of the time interval between two events defined by predetermined pedal positions or pedal actuations. Only the braking manoeuvre in question and/or the pedal actuations preceding this braking manoeuvre are taken into account for this purpose. The expression xe2x80x9cbraking manoeuvrexe2x80x9d used herein covers all processes in the time period between the displacement of the brake pedal from its unactuated position of rest and the subsequent return of the brake pedal to this position of rest which can, for example, be detected from the switching position of the brake light switch.
Various independent methods are contemplated for the adaptation of the triggering sensitivity of the automatic braking operation. Each of these three methods can therefore be applied by itself or in combination with another or both of the other methods for the adaptation of the triggering sensitivity.
A first of the methods according to the present invention is based on evaluation of the speed of return of the accelerator pedal. In emergency situations, the first reaction is a sudden return movement of the accelerator pedal because the driver reduces the driving power of the vehicle. At high return speeds of the accelerator pedal, the threshold value for the speed of actuation of the brake pedal is lowered. A slow, progressive reduction of the driving power of the vehicle, however, rather leads to the inference or conclusion that the driver is in control of the driving situation. Through the raising of the threshold value, the triggering of the automatic braking operation is therefore shifted into the range of higher brake pedal actuation speeds.
In a second method according to the present invention, the waiting time between the reaching of the idling position of the accelerator pedal and the actuation of the brake is measured. An actuation of the brake can be detected from the switching position of the brake light switch. If there is a long period of time between these two events it can be concluded that the vehicle is running down to a standstill under control, and the triggering threshold for the automatic braking operation can be raised.
In a third method according to the present invention, the actuation time between the commencement of the brake actuation, detected by the switching of the brake light switch, and the exceeding of a predetermined speed threshold value for the speed of actuation of the brake pedal is measured. A long period of time then leads to the conclusion that the driver is ready to brake, because he has already placed his foot on the brake pedal, but still delays application of the brake. xe2x80x9cSportingxe2x80x9d drivers tend to operate the brake vigorously after a waiting phase of this kind, although target braking is effected. The triggering threshold is therefore raised with increasing time between the events.
The adaptation of the triggering sensitivity to the driving situation is effected by factors which are derived from a characteristic diagram and by which a predetermined threshold value for the speed of actuation of the brake pedal, or a threshold value, derived from a predetermined threshold value, for the speed of actuation of the brake pedal is multiplied.